Dynamically change project used in a SQL query - dynamic

Question

I am using BigQuery, Standard SQL, and I want to dynamically change parts of the FROM clause, such as the project id. I have been looking for a solution for this the last 3 years - the problem has been that parameters cannot be used as inputs in the FROM clause. The benefit would be to create a stored procedure, where the project id can be passed in as an argument and can query the appropriate project. The projects would have the same datasets and table names - this would be our way of building a Master query for easy development and implementation. Instead of changing 15 clients' views, we can change the Stored Procedure once and it will push out the changes to all clients' views. However, I have always gotten hung up on dynamically changing the FROM clause!
For example:
DECLARE ProjectId STRING DEFAULT 'test_project';
SELECT col_1 FROM `#ProjectId.Dataset.Table`;
would always error out due to parameters not being able to be used in the FROM clause. However, I saw a related post on using dynamic SQL to overcome this obstacle. I've been looking into the EXECUTE IMMEDIATE function within BigQuery, as this is what has been cited to be a solution. From that post I attempted to implement in several ways:
Attempt #1:
DECLARE ProjectId STRING DEFAULT 'test_project';
EXECUTE IMMEDIATE CONCAT(
"SELECT * FROM ", #ProjectId, ".DataSet.`Table` " )
^ This gives an error "Query error: Undeclared query parameters at [2:19]"
Attempt #2:
EXECUTE IMMEDIATE CONCAT(
"SELECT * FROM ", #ProjectId, ".DataSet.`Table` " )
USING 'my-project' as ProjectId, 'my-dataset' as DataSet;
^ which gives the error "Query error: Undeclared query parameters at [1:19]"
Third and final attempt was to try declaring the parameter within the EXECUTE IMMEDIATE:
EXECUTE IMMEDIATE CONCAT(
"DECLARE ProjectId STRING DEFAULT 'test_project'; ",
"SELECT * FROM ", #ProjectId, ".DataSet.`Table` " )
USING 'my-project' as ProjectId, 'my-dataset' as DataSet;
^ which, you guessed it, results in the same error "Query error: Undeclared query parameters at [1:19]"
I am reaching out to see if anybody has had success with this? I see the value in the Dynamic SQL statements, and have read the documentation and some examples, but it still doesn't seem to work when trying to dynamically change the FROM clause. Any help is much appreciated, willing to try whatever is thrown out - excited to learn what can be done!

Answer 1

Just remove #:
DECLARE ProjectId STRING DEFAULT 'test_project';
EXECUTE IMMEDIATE CONCAT(
"SELECT * FROM ", ProjectId, ".DataSet.`Table` " )